U.S. Secretary of State Rex Tillerson is due to meet on January 22 with top British officials in London, the first leg of a nearly week-long trip to Europe that will also take him to Paris, Warsaw, and the World Economic Forum in Davos, Switzerland.
An official has said that Iran would dominate Tillerson's meetings with US allies.
The trip comes amid behind-the-scenes negotiations over the fate of a landmark agreement to curb Iran's nuclear program in exchange for easing crippling international sanctions targeting Tehran.
"As you know, we really emphasize close coordination with the British in particular and the French in our efforts to close the gaps in [the agreement] and in [the] next steps on how we curtail Iranian malign influence in the region," a State Department official told reporters on January 19. "So I think that'll be a very high priority in his conversations."
Earlier this month, US President Donald Trump said that he wanted to work with European allies and Congress to fix what he called "disastrous flaws" in the 2015 Iran deal signed under his predecessor, Barack Obama.
Trump warned that Washington would withdraw from the deal if it is not strengthened within four months.
Tehran has ruled out any changes in the agreement, while the other signatories -- Britain, France, Germany, China, and Russia -- have closed ranks in support of the accord.
Ahead of a meeting of European Union foreign ministers in Brussels, French Foreign Minister Jean-Yves Le Drian said on January 22 that Trump's demands "sometimes look like ultimatums."
Le Drian also said that EU ministers would stay "firm" on the need to preserve the agreement, which the minister called "an essential element" of global efforts against nuclear proliferation.
Iran insists its nuclear program is only for peaceful purposes, while the United States and other countries claim it has been trying to develop nuclear weapons.
In London, the secretary of state visited the new U.S. Embassy, which opened last week.
Trump had been expected to preside over the opening ceremony for the embassy but the president dismissed that idea, citing the billion-dollar cost of the diplomatic mission, among other things.
The State Department said Tillerson would also hold talks with U.K. Prime Minister Theresa May, national security adviser Mark Sedwill, and Foreign Secretary Boris Johnson to discuss cooperation on Iran, Syria, Libya, North Korea, and Ukraine.
From London, Tillerson will travel to Paris on January 23 for talks on many of the same subjects with Le Drian.
In an interview to be published on January 22,the French minister said he would visit Iran on March 5 to discuss Tehran’s ballistic-missile program and the 2015 nuclear deal.
Le Drian told the Le Figaro daily that France "wishes to bring up [Iran's] destabilizing military influence in the Middle East, its financial support for Lebanon's Hizballah and for the Huthi [rebels] in Yemen."
After Paris, Tillerson will spend two days in Davos shadowing Trump at his first visit as president to the annual economic forum.
By January 26, he will be in Poland for more talks with senior officials on security and economic matters.
The U.S. official said that Tillerson would be discussing the U.S. military presence in Poland, which has hosted American and other allied troops following Russia's 2014 seizure of Ukraine's Crimean Peninsula and its backing of armed separatists in eastern Ukraine.